High-Speed Sailing

Let's take a look at Monofoil:

http://www.monofoil.com/boat/index.php

This is a fascinating craft; I hope it is soon completed and sailing. If you examine their website you will see that it has a leeway resisting hydrofoil to windward and a wing to leeward. Between those two is an aircraft like cockpit. Note that the leeward wing is not parallel to the hydrofoil; rather it is inclined further to windward to produce lift and raise the cockpit out of the water at speed. The advantage is that the water's drag will be reduced, but there are certain disadvantages. (This is not a criticism since any craft will be a series of compromises.)

Note that Sailrocket, Paravane and my designs set the airfoil parallel to the hydrofoil to achieve zero roll. Any craft with a kite can only achieve zero roll with the kite in one exact position. Windjet, when outfitted with a wing, shows the craft rolling to windward in order to raise the lee hull out of the water, but I don't know how that is being done.

If the airfoil is used to roll the craft to windward (Monofoil and possibly Windjet) the craft does not have true roll stability, but some means must be used to roll the craft the desired amount and no more. I suspect that for Monofoil, the pilot or co-pilot would control this function. Sailrocket uses the arm that the wing sits on, as an airfoil operating in surface effect, to roll the craft to windward and lift the lee plane out of the water at speed. I believe this is the best way to roll the craft (independent of the airfoil that drives it).

I like the fact that Monofoil is set-up to sail on both tacks. Of the recent top contenders; windsurfers, kite sailors, Longshot (Trifoiler) and Hydroptere are all capable of sailing both tacks. My own designs have always been capable of sailing both tacks and if I were involved with a speed record attempt, I would want to run a craft that could go both ways. Perhaps the rules should read that the record will be the average of a port tack and a starboard tack.

One other observation I'd like to make; note that Monofoil has its payload (skipper, etc.) between the airfoil and hydrofoil. Sailrocket, kite sailors, Le Projet Dared and Windjet, all have their payload to windward, near the hydrofoil. Paravane takes the opposite approach and has its payload to leeward, positioned with the airfoil. Paravane's approach necessitates keeping the paravane in contact with the surface of the water at all times or the craft will flip. Additionally, if the paravane is not designed to instantly shed any trash (seaweed, plastic bags, etc.) it will flip if it snags sufficient debris, since its "lift" will disappear. I watched this happen to Trifoiler; Ketterman was sailing it at speed (around 30 knots) when the windward side suddenly leapt out of the water, the craft rotated abruptly off the wind and it crashed back to the surface. I asked Ketterman what happened and he said he thought he snagged a piece of kelp (losing down-force on the windward side).

I have experimented with positioning the payload to windward (at hydrofoil) to leeward (at airfoil) and in between. While any position can be made to work, I have found the best position to be to windward. Note that if my leeway resisting hydrofoil loses "lift" by snagging trash, by pulling out of the water while going over a wave trough, or even if it breaks off, the craft will not go out of control, it will merely slide sideways. You can see a demonstration of this in my video (follow the Sailien video link).

Bob